Electron transport phenomena in plasma devices with E x B drift

A review of plasma devices involving electron drift in crossed electric and magnetic fields (E x B drift) and electron transport phenomena is presented. There are two important peculiarities of E x B system: possibility to maintain a large electric field in a quasi-neutral plasma which allows transport of relatively large intensity beam of charged particle and an efficient impact ionization due to closed electron drift. Several technological applications of devices based on electron drift in E x B field are under development, including plasma immersion ion implantation, energetic deposition of materials, magnetron sputtering, and plasma propulsion. Despite very different applications, the underlining physics of operation of these devices is very similar. One of the important physical phenomena is the electron transport across a magnetic field. Experimental and theoretical study reveals that electrons undergo anomalous transport and several possible mechanisms are proposed and studied previously. Anomalous electron transport mechanisms such as Bohm diffusion and near-wall conductivity are reviewed and assessed for two E x B devices, namely magnetron and Hall thruster. A modified model of the near-wall conductivity that takes into account various sheath effects is developed. It is shown that an axial electric field in the sheath can significantly affect the near wall conductivity.